Plot hole: When the warden comes into the cell the morning after the escape, the poster covering the hole is fastened down on all four corners - impossible to do after squeezing into that small hole. [On the DVD commentary, the director confirms that this was a movie "cheat".]

Red: There's not a day goes by I don't feel regret. Not because I'm in here, or because you think I should. I look back on the way I was then: a young, stupid kid who committed that terrible crime. I want to talk to him. I want to try and talk some sense to him, tell him the way things are. But I can't. That kid's long gone and this old man is all that's left. I got to live with that. Rehabilitated? It's just a bullshit word. So you go on and stamp your form, sonny, and stop wasting my time. Because to tell you the truth, I don't give a shit.

When Red is sitting under the oak tree in 1967 and pulls the money out of the envelope, the top bill is signed by Nicholas F. Brady, who was Secretary of the Treasury September 1988 - January 1993. It's less about reading the handwriting as noting the different appearance of different signatures from different eras.

There are many references to the number 237 in the movie. For instance, this is the number of Red's cell, and these digits are on Andy's prison I.D. This number makes appearances throughout Steven King stories, the most famous one being the room where the murders take place in "The Shining".